1. Field of the Invention
This invention relates in general to a data transmission method, and more particularly to a method for transmitting video images in a data communication network.
2. Description of Related Art
In the prior art, several methods for the transmission of video images in a data communication network are known. A feature typical of these methods is that the image is compressed in some way before transmission to allow faster transmission. Among the prior-art compression methods are, e.g., MPEG (Moving Pictures Experts Group), and H.261 and H.263 standardized by ITU (International Telecommunication Union, ITU).
The prior-art compression methods are characterized in that, instead of transmitting complete frames, only the differences between successive frames are transmitted. Moreover, predictive coding is used to reduce temporal redundancy, and modification coding to reduce spatial redundancy.
A problem with the prior-art methods is that they apply compression to entire frames and transmit all differences between successive frames. Consequently, the amount of data to be transmitted remains too high for the needs of narrow-band data communication networks. For example, if an MPEG-compressed video image with a resolution of 388*288 is transmitted over a GSM network, the transmission of a single frame may take as long as 15 seconds.
It can be seen then that there is a need for a method for processing a video image so that the image can be readily transmitted even in a narrow-band data communication network, such as a GSM network.